As a satellite position measurement technology for receiving and analyzing radio waves from a plurality of satellites and detecting a position of a receiver (hereafter called “mobile station”), a single position measurement system for measuring position by a solo mobile station even if the measurement error is large, and a relative position measurement system for accurately determining the position of a mobile station using the correction data from a reference station of which position is known, are available.
In the relative position measurement system, the position measurement accuracy is restricted by the linear distance between receivers, which is the so called “base length”.
For example, in the case of a relative position measurement system which measures the position independently using the C/A code of GPS (Global Positioning System) and corrects the position using the correction data, the limit of the base length, when the uncertainty of orbit information of the satellite and the error due to the ionosphere and atmosphere etc. are approximately the same for each receiver, is about 100 km or less, and an error can be offset within this range, so an improvement of position measurement accuracy in the relative position measurement system can be expected.
On the other hand, in the case of a system which analyzes the base line using a carrier phase so as to improve the position measurement accuracy, the limit of the base line is short, about 10 km or less, but the position measurement accuracy improves dramatically since a carrier phase, which is sufficiently shorter than the C/A code, is used [e.g. see the new edition of GPS-Precision Positioning System by Satellites (issued by Japan Survey Association)].
An example of a relative measurement system for measuring a relative displacement of a mobile station using radio waves from satellites has been disclosed in Japanese published patent application (2001-281323), and this can measure the displacement at an accuracy equivalent to a kinematic system.